This invention relates to compositions for use in fracturing formations such as oil or gas wells, to methods of making said compositions and to fracturing of underground formations using such compositions.
A process of hydraulic fracturing of an oil or gas well to improve its productivity is well known. Essentially the process involves the injection of a fluid down the wellbore and into the productive formation at sufficient rate and pressure that the formation rock fractures from the induced stresses. A proppant, such as sand or small particles of sintered bauxite, is added to the fluid and carried into the formation fracture. This proppant prevents closure of the fracture when hydraulic pressures are released, thereby leaving a conductive flow channel from the wellbore deep into the rock matrix.
Traditionally the fluid used for the purpose of hydraulic fracturing has been oil, water, or an emulsion of these two liquids. An efficient fracturing fluid should possess good proppant transport characteristics, which characteristics are related to the viscosity. Generally the viscosity should be high in achieving the goal of wider and larger fractures, for fluid loss and for efficient proppant transport. A wide range of additives are also used to enhance the rheological properties and/or the chemical properties of the fluid. Such additives include viscosifiers, friction reducing agents, surface active agents, fluid loss control additives and the like.
Recently, the application of aqueous methanol, either by itself or in conjunction with gases such as carbon dioxide or nitrogen, has been established due to certain advantageous properties of this fluid. Advantages of methanol include its low freezing temperature for use with liquid CO.sub.2, compatibility with water-sensitive formations, and low surface tension for improved load fluid recovery.
A disadvantage of the use of methanol is that it has usually been found necessary to include a percentage of water to act as solvent for the gellants. The amount of water is usually in the range of from 10% by 25% by volume of the alcohol. Without this water, a satisfactory viscosity increase is not obtained with most natural gums or synthetic polymers. This produces difficulties in the case of those formations where water itself may be regarded as forming a blockage in the formation. The use of anhydrous or substantially anhydrous alcohol is desirable for some purposes but, to date no wholly satisfactory gellant for use in anhydrous alcohol has been found.
Attempts have been made to provide gellants for use in anhydrous alcohols. For example U.S. Pat. No. 3,954,626 discloses a well treating gel comprising substantially anhydrous lower alcohols gelled by the use of hydroxy propyl methyl cellulose. U.S. Pat. No. 4,012,327 discloses substantially anhydrous lower alcohols thickened but not necessarily gelled by the use of aminomethylated polyacrylamide of molecular weight up to around 1 million. This composition appears to be a simple thickened liquid not having the advantageous flow properties of non-Newtonian fluids, e.g. true gels.